Messages in this thread | | | From | Will Deacon <> | Subject | [PATCH 0/2] arm64: Only call into preempt_schedule() if need_resched() | Date | Tue, 27 Nov 2018 19:45:00 +0000 |
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Hi all,
This pair of patches improves our preempt_enable() implementation slightly on arm64 by making the resulting call to preempt_schedule() conditional on need_resched(), which is tracked in bit 32 of the preempt count. The logic is inverted so that we can detect the preempt count going to zero and need_resched being set with a single CBZ instruction.
Consequently, our preempt_enable() code (including prologue/epilogue) goes from:
40: a9bf7bfd stp x29, x30, [sp, #-16]! 44: 910003fd mov x29, sp 48: d5384101 mrs x1, sp_el0 4c: b9401020 ldr w0, [x1, #16] 50: 51000400 sub w0, w0, #0x1 54: b9001020 str w0, [x1, #16] 58: 350000a0 cbnz w0, 6c 5c: f9400020 ldr x0, [x1] 60: 721f001f tst w0, #0x2 64: 54000040 b.eq 6c // b.none 68: 94000000 bl 0 <preempt_schedule> 6c: a8c17bfd ldp x29, x30, [sp], #16 70: d65f03c0 ret
to:
40: a9bf7bfd stp x29, x30, [sp, #-16]! 44: 910003fd mov x29, sp 48: d5384101 mrs x1, sp_el0 4c: f9400820 ldr x0, [x1, #16] 50: d1000400 sub x0, x0, #0x1 54: b9001020 str w0, [x1, #16] 58: b4000060 cbz x0, 64 <will+0x24> 5c: a8c17bfd ldp x29, x30, [sp], #16 60: d65f03c0 ret 64: 94000000 bl 0 <preempt_schedule> 68: a8c17bfd ldp x29, x30, [sp], #16 6c: d65f03c0 ret
Will
--->8
Will Deacon (2): preempt: Move PREEMPT_NEED_RESCHED definition into arch code arm64: preempt: Provide our own implementation of asm/preempt.h
arch/arm64/include/asm/Kbuild | 1 - arch/arm64/include/asm/preempt.h | 78 ++++++++++++++++++++++++++++++++++++ arch/arm64/include/asm/thread_info.h | 13 +++++- arch/s390/include/asm/preempt.h | 2 + arch/x86/include/asm/preempt.h | 3 ++ include/linux/preempt.h | 3 -- 6 files changed, 95 insertions(+), 5 deletions(-) create mode 100644 arch/arm64/include/asm/preempt.h
-- 2.1.4
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